Study of Uranium Removal from Groundwater by Supported Liquid Membranes

The separation of uranium from synthetic Hanford site groundwater by liquid-liquid extraction and by supported liquid membranes (SLM) was atudied. Bis(2,4,4-trimethylpentyl) phosphinic acid, HDTMPeP], contained in the commercial extractant Cysnex 272, was selected for the membrane carrier because of its selectivity for uranium over calcium and magnesium. n-Dodecane was used as diluent and polypropylene membranea were used as the support. A water soluble complexing agent, 1-hydroxyethane-1,1-diphoaphonic acid, HEDPA, was used as atrlpping agent.

The permeability coefficient of U(V1) was evaluated from a detailed study of the permeation of U(VI) through flat-sheet SLMs as a function of the membrane carrier concentration. The diffusion coefficient of the uranium complex in the organic phase was also evaluated from permeation experiments performed under loading conditions. Experiments were also carried out with Cs(II) and Fe(III) to measure the membrane selectivity for U(VI) over these two cations. A very high selectivity of U(VI) over Cs(II) was obtained, due the very low distribution ratio of Cs(II) with the extractant HDTMPeP] (thermodynamic selectivity). In the case of Fe(III), a good selectivity was also obtained, due to the slow reaction of Fe(III) species with HDTMPeP] (kinetic selectivity).

The possibility of concentrating U(VI) in the strip solution by a factor of at least 10³ has been experimentally demonstrated by properly designed distribution experiments.